Abstract 14551: Isoproterenol Induced Protein Phosphatase2Ce Up-Regulation Suppresses Cardiac Contraction
Protein phosphatase 2Ce (PP2Ce) is a novel serine/threonine protein phosphatase specifically targeted to sarcoplasmic reticulum (SR) membrane in cardiomyocytes. PP2Ce has a potent activity towards phospholamban, a significant impact on beta-adrenergic stimulated cardiomyocyte contractility. Further more, PP2Ce expression is significantly induced at protein level by acute isoproterenol (ISO) treatment without affecting the mRNA level. Here we assessed the hypothesis that PP2Ce is an important player in beta-adrenergic mediated regulation in heart. First of all, we investigated with coimmunoprecipitation analysis whether PP2Ce links to some SR membrane protein. The result revealed that PP2Ce interacted with phospholamban in mouse heart. The interaction was enhanced in transgenic heart overexpressing PP2Ce. Both basal and ISO induced PP2Ce protein expressions were enhanced by acute treatment of proteasome inhibitor MG-132 and suppressed by acute treatment of protein synthesis inhibitor cycloheximide, indicating that the PP2Ce undergoes rapid protein turn-over and its up-regulation by ISO was largely contributed by protein degradation via proteasome pathway and protein synthesis. We look further into the signaling mechanisms involved in ISO induced PP2Ce regulation. Western blotting results showed that PP2Ce expression was rapidly increased by cAMP analogue forskolin and PKA-specific agonist 6-Bnz-cAMP, and ISO induced PP2Ce up-regulation was inhibited by PKA inhibitor H89, suggesting that cAMP/PKA pathway was directly involved in ISO induced PP2Ce regulation. Finally, we determined the effect of PP2Ce expression on ISO stimulated cardiac contraction using isolated heart. PP2Ce protein in PP2Ce transgenic mouse heart was increased within 30 min of ISO stimulation correspondently. Contractility of the PP2Ce transgenic mouse heart as measured from +dP/dt max was significantly reduced compared with that of wild type mouse heart, suggesting that ISO induced PP2Ce up-regulation suppressed cardiac contractility. In conclusion, ISO induced PP2Ce up-regulation via cAMP/PKA pathway may play an important role as another SR targeted negative feedback regulation for beta-adrenergic signaling and cardiac contractile regulation.
- © 2011 by American Heart Association, Inc.